Exploring the features of Firebug, with code examples covering using the console, timing code, stack traces, debugging and breakpoints, profiling, tracing HTTP requests. An excellent overview of Firebug's functionality
A BetterExplained article that discusses how to reduce the initial load time of JavaScript files. Covers measuring load times, and a number of approaches to delaying the loading of a JavaScript file. Also covers minifying JavaScript and maintaining a debug version of code. Also covers an AJAX onLoad pattern to dynamically include JavaScript after page load, and HTTP caching of external JavaScript files